1. Field of the Invention
The present invention generally relates to fields of study in three broad categories: ion separation; plasma physics; and microgravity processing. Within the category of ion separation, relevant sub-fields include: mass spectroscopy, ion implantation, and isotope separation. Within the category of plasma physics are relevant sub-fields of: thermal spray and magnetohydrodynamics. Under the category of microgravity processing lie the sub-fields of: heating systems and element separation techniques. Also pertinent to this invention, but well known to those skilled in the art, are the sciences of: optics, solar power generation, material crushing or grinding, chemistry, magnetics, electrostatics, radio-frequency electromagnetics, radiative cooling, and static and dynamical mechanics. The present invention involves each of these fields, and more particularly relates to a process employing these technologies to separate isotopes in microgravity using solar power as the energy source.
2. Description of the Prior Art
In the field of mass spectroscopy, a sample is ionized and sputtered from the matrix being studied, through bombardment by another ion such as oxygen or argon. A sample analyzer segregates isotopes through the application of a magnetic field. As ions of charge q, with a velocity v and mass m pass through a magnetic field of strength B, they experience a force perpendicular to the field direction according to the Lorentz force, F=qvxB (italicized quantities are physics variables, and bolded quantities are vectors; F is force, a is acceleration, m is mass, q is electron charge, v is velocity, B is magnetic field strength, E is electric field strength, and x is the cross product operator). This force causes an acceleration in a direction normal to the original velocity according to Newton""s law a=F/m. Because different ions have different masses, the acceleration they receive is different. This effect is exploited to separate out the various elements and isotopes of the matrix under study. Suitable collectors monitor the amount of charge impinging at the location associated with various isotopes, providing an indication of their presence, and an approximate indication of their relative abundance. Prior art in the field of mass spectroscopy include U.S. Pat. No. 4,066,895 to Iwanaga; U.S. Pat. No. 4,174,479 to Tuithof et al., U.S. Pat. No. 5,220,167 to Brown et al., U.S. Pat. No. 3,443,087 to Robieux et al., and U.S. Pat. No. 3,772,519 by Levy et al. This technique of magnetic separation is widely used in many fields, as will be discussed below. The current invention also uses magnetic separation as a constituent component, and as such its understanding of this field is crucial to understanding this invention. However, the means of ionization and collection are substantially different.
In the field of ion implantation, used typically for semiconductor manufacture and for impregnation of specialty materials, a gaseous molecule containing the element of interest is ionized using a radio frequency plasma. The plasma field causes dissociation of the molecule, and causes an excited state of the element to be implanted. All excited species of charge q are then accelerated using electrostatic fields of strength E according to the equation F=Eq. The accelerated ions are collimated and passed through a magnetic field to separate the various isotopes. A suitable shutter system is employed to select the ion of interest, which is then allowed to proceed toward the substrate to be implanted with this ion. However, along the beam path, between the separation magnet and the substrate, dynamic electric fields, oriented typically in two perpendicular directions to the beam axis, are employed to deflect the beam slightly. This deflection is used to cause the beam to be scanned across the substrate, typically with the desire to uniformly cover the substrate area. Once the beam arrives at the substrate, typically with a relatively high velocity and relatively low density, the ions will impinge upon the surface, and penetrate to a distance determined by the beam energy, the ion mass, the angle of incidence, and the atomic mass and crystal orientation of the substrate. Several patents in this area include U.S. Pat. No. 4,841,143 to Tamura et al., and U.S. Pat. No. 5,751,002 to Ogata et al. The present invention uses the principles of dynamically scanning a beam using electric fields, and as a preferred embodiment, will use shutters to select a specific isotope. However, the method of ionization is substantially different, and the means of collection are substantially different.
Isotope separation, as a field of study, is principally used to enrich uranium with the isotope of atomic weight 235, relative to the much more abundant U238 . A number of patents in this field demonstrate a wide variety of techniques for achieving isotope enrichment, such as U.S. Pat. No. 3,935,451 to Janes, U.S. Pat. No. 3,940,615 to Kantrowitz, U.S. Pat. No. 4,202,860 to Miyake et al., U.S. Pat. No. 4,726,967 to Arendt et al., U.S. Pat. No. 5,024,749 to Snyder et al., U.S. Pat. No. 4,399,010 to Lyon et al., U.S. Pat. No. 5,422,481 to Louvet, U.S. Pat. No. 4,757,203 to Gil et al., U.S. Pat. No. 5,224,971 to Mukaida et al, and U.S. Pat. No. 3,953,731 to Forsen. Among the various techniques are those which use a linear direction of ion travel, and those which employ a spiral or cyclotron ion movement. In all cases, the uranium, or other element, such as zirconium, is first ionized using one of several different methods. The first broad class of ionization techniques involves first evaporating the material, and then ionizing it using radio-frequency (rf) energy or tuned laser radiation. Evaporation is accomplished with any of several techniques, such as Joule heating, laser bombardment or ion sputtering. Ionization with rf energy will typically excite all isotopes of the element of interest. However, with laser ionization, the frequency of radiation can be selected to preferentially ionize one isotope over another. This appears to be the preferred method in many patents, since it allows separation to be accomplished using electric fields, instead of magnetic fields, although both can be found in the patent records. Once the moving (linear or cyclotron) isotopes are ionized and separated by either electric or magnetic fields, they are collected at surfaces that are temperature controlled to allow condensation. This invention uses the techniques of collection of the separated ions on suitable surfaces. However, the heating method is substantially different, and there is substantially greater flexibility envisioned for the collection techniques, as will be described in the detailed description below.
The application of very rugged coatings of metal or ceramic is the goal of thermal spray. In each form, the material to be deposited is supplied in a powdered form carried in a stream of gas, such as nitrogen. The small particles of material are plasticized, melted, or ionized, depending on the energy supplied. This energy may be from the combustion of a reactive fuel with oxygen or from an electric arc. The heated particles of metal or ceramic are then carried to the substrate to be coated by the carrier gas, or by the velocity of the exit gasses from combustion. These particles then coat the surface of the substrate, preferably with very little surface reaction, and typically produce a very dense coating. Representative patents in the field of thermal spray include U.S. Pat. No. 3,892,882 to Guest et al., and U.S. Pat. No. 5,716,422 to Muffoletto et al. The current invention does not use a carrier gas, use combustion, or electric arcs, but it is a preferred embodiment of this invention that the material collected not interact with the substrate; thereby relating to this invention. Also, thermal spray is typically done in atmospheric environments, whereas the current invention is processed in the relative vacuum of space.
The principles of magnetohydrodynamics involve the motion of a charged medium through a magnetic field. In a typical embodiment, the momentum of the moving medium imparts a backward electromotive force which can be used for power generation. In another form, more germane to this invention, the magnetic field can be used to selectively alter the trajectories of the moving medium, which may be a plasma of ionized isotopes, for example. In this way, magnetohydrodynamics is similar in principle to mass spectroscopy. A patent describing this method is U.S. Pat. No. 4,737,711 to O""Hare. This patent also describes a method of element separation.
To prevent interaction between the elements of a plasma and container walls, magnetic confinement is typically used. This may range from the complex toroidal magnetic fields used in tokamak style fusion reactors, to simple xe2x80x9cpicket fencexe2x80x9d style bar magnets placed around the plasma. In either case, the principle involved is that the charged particles (ions and electrons) in the plasma will be deflected away from the magnets through the Lorentz force. Examples of magnetic confinement are common; some illustrative examples are taught in U.S. Pat. No. 4,534,842 to Arnal et al.; U.S. Pat. No. 4,937,456 to Grim et al., U.S. Pat. No. 4,093,427 to Schlenker, and U.S. Pat. No. 4,672,615 to Kelly et al.
A materials processing environment in a circular orbit around a massive body is essentially in a free-fall, where the effects of static gravity, such as are felt on the surface of such a massive body, are not felt, or are very small. Such a microgravity environment has certain advantages for materials processing. The sedimentation or settling of materials of varying densities in a suspension does not occur; allowing the formation of more homogenous materials in orbit than on the surface of a planet or planetoid. The relatively less stringent requirements for fixturing are another feature exploited in some patents on microgravity processing. A sample of microgravity processing patents is U.S. Pat. No. 5,196,999 to Abe. Several of these advantages are important to this invention as will be described in the sections below.
Many methods for the separation of chemical elements or molecules in space have been proposed and studied. For the most part, these include the use of reagents, catalysts, and consumable chemicals which must be brought from a planet such as Earth, at great expense. Furthermore, the equipment for these processes tends to be very expensive and intricate, requiring significant maintenance. It is a significant advantage of this invention that it requires no reagents, catalysts, or consumable chemicals, no reaction vessels, and very little maintenance. This current invention has very little in relation to these chemical means of element extraction, but this area is included for completeness. References to these schemes can be found in U.S. Pat. No. 4,737,711 to O""Hare (noted above), U.S. Pat. No. 5,374,801 to Leung, and U.S. Pat. Nos. 5,096,066 and 5,153,838 to Kindig.
According to the present invention, there is provided a process and apparatus that achieves continuous-feed all-isotope separation in microgravity using solar power. In this process, a stream of material, such as crushed rock or waste materials, is given a velocity and directed on a substantially linear path. This may come from an impeller, a solar furnace, a pair of electric field (electrostatic) acceleration grids, or other device which imparts a velocity to the stream, and may be fed from a hopper of material, or directly from a bore hold in an asteroid, for example. Once the material is given a velocity, it is heated and ionized along its path by concentrated sunlight, radio-frequency ionizing radiation, and/or laser irradiation. A magnetic confinement scheme to maintain the cross sectional area of the beam can be used to counteract the effects of thermal diffusion and self-scattering. Physical confinement can also be used to maintain a tight beam of material, possibly at one or more locations along the stream path. Solar or laser radiation not absorbed by the stream is optionally collected by suitable placement of solar panels which convert the radiant energy into electrical energy available for use in the operation of the apparatus.
The ionized stream is deflected using electrostatic fields, which are disposed around the beam such that a plurality of deflection orientations and angles can be achieved. This serves three purposes: that of separating ionized from nonionized material; separating out individual isotopes from the ion stream; and for providing additional attitude control for the entire structure by allowing some of the stream to exit the apparatus uncollected. Optional acceleration or deceleration using additional electrostatic fields may also be employed. The various isotopes of the stream are separated differentially depending on their charge and mass. The individual streams of separated isotopes can then be collected in a variety of ways, including, but not limited to: simply impinging on a planar surface; the use of slits or shuttering for very high purity; the use of a moving substrate to allow spatial patterning of the deposited material; implanting of the ions for material preparation; combining isotopes or layering them to produce composite or compound materials; and cooled condensation of volatile gasses. The neutral (nonionized) stream can be collected separately, for its reprocessing value, as well as its momentum. The waste heat from the neutral stream, and the collected isotopes can be used in a closed loop thermal generator for addition production of electrical or mechanical energy.
In view of the above, the present invention provides numerous benefits and structural and processing options. Any material can be fed into the apparatus for separation into isotopes. For example, one application for the apparatus is waste reprocessing in a recycling loop. Continuous operation of this process is inherent to the apparatus, and only requires a steady input stream of raw materials. Multiple isotopes can be separated from the input stream. In fact, every single isotope within a given sample can theoretically be ionized and extracted. Isotope separation can be accomplished in a single pass, without cyclotron resonance or other vibrational methods for separation. Collection surfaces can optionally be tilted at a low angle to the incident stream of purified isotope, thus reducing the penetration depth and spreading the heat across a much larger surface, minimizing cooling requirements. This makes collection of volatile materials easier, and prevents reaction between beam and substrate. Residence time and temperature in the heat zone can be adjusted with mirrors and optics to allow sufficient energy to fully vaporize any material.
The heat made available with this apparatus from sunlight is sufficient to separate out most molecules into atomic elements, which are further ionized to produce a charged state. The heating is arranged so as to ionize the material as completely as possible, maintaining a high temperature, which tends to prevent the formation of molecules. The apparatus also provides for the ionizing radiation (sunlight) to be directed substantially along the material stream, and at a multiplicity of angles. This increases the cross section for absorption, thereby allowing very high efficiency for ionization fraction. The mirrors can allow for the gradual heating of the material stream along its line of travel. Tunable ionization through rf or lasers allows optimization of the isotope separation to very refractory materials, or other hard-to process ingredients. Broad frequency spectra can be used to excite multiple isotopes across multiple atomic species. Achieving the maximum efficiency of ionization may require a precisely tailored heating profile for a given particle throughout the duration of its transit through the ionization zone, such as may be more concentrated toward the start of the transit, or more concentrated toward the end of the transit. This, and other schemes conceivable by those skilled in the art, can be accomplished through suitable design of the collection mirrors. Multiple sections of alternate heating and confinement can be used to distribute the power requirements, and to maintain a small beam cross section along the path of the material stream. This reduces angular variation in the separated isotopes and provides for greater purity in the collected isotopes.
The Lorentz force deflects the isotopes of the beam differing degrees depending on the charge state and the atomic mass, allowing the isotopes to be collected separately. Beam speed and energy is adjustable with a number of parameters, giving an extremely wide variation in the properties of the separated isotope beams. Because the apparatus can be scaled to essentially any size, the required deflection field strengths can be minimized when input power is low, for example, in orbits distant from the Sun.
Using simple goniometer and translation stages in the isotope streams allows direct writing of highly-purified materials onto any conceivable surface. The use of electrostatic field, parallel to the velocity of the separated isotopes, can be used to reduce that velocity for the purposes of reducing the heat energy delivered to the collection receptacle. Alternatively, the velocity can be increased by reversal of these electrostatic fields to provide for greater penetration of the isotopes. By generating multiple isotope streams, the creation of superlattices with an extremely versatile spectrum of physical and material properties is possible, permitting the replication of almost any conceivable structure.
The axial design with lens and mirrors facing the Sun provides radiation and contamination protection to down-beam components, inherent to the design. The arrangement of the sunlight concentrating and other heating elements is arranged so as to block solar wind from contaminating the stream.
The impeller/feeder pipe design for the input material stream provides for separating out particles of various size, and directing them to kinetic energy adding devices and nozzles such that each of these various streams is optimized for desired velocity and minimal spreading of the material stream. Multiple nozzles, each feeding a fraction of the material stream, which may be homogenous or heterogeneous, can be used to optimize the mixing and minimize the self-scatter, spreading, and range of velocities of the entire beam. Use of a solar furnace may be used in place of an impeller to eliminate moving parts, and impart a thermal velocity to the material stream. Preheating with a solar furnace also lessens the heating requirements along the material stream path.
The momentum and torque imparted to the initial material stream can be arranged so as to allow control of the entire apparatus in a desired orbit and attitude toward an energy source, like the Sun. The apparatus enables the conservation of total momentum of the material stream, allowing it to remain in a substantially stationary position with respect to a desired relative location in space. This provides the opportunity to have the apparatus placed in orbit around a body other than the Sun, while using lightweight movable mirrors to direct the solar radiation to this invention. The entire structure can be moved through controlled imbalances in the impeller motion, the separation elements, or magnetic field placed in the path of the ion streams. A suitable controller can use this ability to self-align the structure to a desired orientation, using only internal signals such as gyroscopic or stellar position-determined, eliminating or greatly reducing the need for chemical or electric propulsion requiring fuel.
The apparatus of this invention can be used to make many of the materials for replicating itself, thus approximating a von Neumann machine, which makes it suitable for highly-automated material processing and fabrication facilities. Sunlight is used directly in the processing of material, and indirectly or optionally in the electric power generation for individual components, such that auxiliary and exhaustible energy sources are unnecessary. Alternate sources of electromagnetic radiation can be used to power the apparatus, including laser radiation coaxial and coincident with the material stream. Sunlight and material inputs to this invention are very nearly used in their entirety so that waste is very low, and processing efficiencies approach 100%, assuming neutral beam constituents are reprocessed. By collecting numerous elements simultaneously, the apparatus avoids the need for separate chemical processing units designed for specific classes of molecules. The lack of requirements for externally supplied reagents allows the apparatus to be operated at very low ongoing costs, and the lack of moving parts provides for very long time between failures.
The apparatus and process can be used either in free-floating orbit, or rigidly attached to a planetoid with modification to the arrangement of mirrors and impeller/feeder tube assembly. Rigidity and inertia to rotation movement are optimized by providing a substantially uniform distribution of moments about the center of mass, and designing the structure to have a roughly spherical envelope or outer perimeter, such perimeter including impeller devices, a neutral particle receptacle and cooling apparatus, and solar collection panels. Because of the vacuum of space, the apparatus need not include a container, need not have a controlled atmosphere, and concerns about contamination are greatly reduced, compared to devices designed for an environment with atmospheric pressure. The use of structural members is greatly reduced by the superstructure design such that tensile loads balance the momenta of sunlight and the material and isotope streams. The threefold symmetry of the preferred embodiment is not a restriction of the design. Higher order symmetry can also be used. Alternatively, the apparatus can be configured to lack symmetry, provided that the overall balance of design considerations is still incorporated, that of positional stability, attitude control, and interdependence of the various components of the system.
While this invention draws from many fields of study, the combination and arrangement of elements allow advantages not possible with existing methods of isotope separation. An advantage of this invention lies in its holistic design concept and unified principle of operation, taking full advantage of mechanical, radiative, thermal, and electrical energies to produce a device capable of low-maintenance, high-reliability operation, with minimal external supply needs, making it especially efficient for remote operation, providing near- geometrically increasing economic returns. These advantages further provide for the raw materials and some of the power needs for construction and manufacturing processes in orbit, without the cost and risk of raising these materials from the surface of a planet or planetoid. It is expected that the realization and implementation of the apparatus and process will greatly facilitate the advance of human utilization and colonization of space.
Other objects and advantages of this invention will be better appreciated from the following detailed description.